1. Field of the Invention
The present invention relates to a path management device that manages information of a communication path (hereinafter, referred to simply as a ‘path’), and to a storing medium for storing a computer program.
Priority is claimed on Japanese Patent Application No. 2007-167398, filed Jun. 26, 2007, the content of which is incorporated herein by reference.
2. Description of Related Art
The Internet is formed by mutually connecting autonomous TCP (Transmission Control Protocol)/IP (Internet Protocol) networks (Autonomous Systems: AS) belonging to individual organizations (such as Internet Service providers (ISP), business organizations, and the like). AS are formed as collections of network connection tools (such as routers and the like) that operate under a common path control policy. A router possesses a routing table and forwards packets based on the routing table. The routing table is formed by a list of path information. The path information contains prefixes (a combination of IP addresses and bit numbers of subnet masks) which are a collection of destination addresses, IP addresses of next hop routers that are used to arrive at the prefixes, and the cost. When path information having a prefix that includes a particular destination address is contained in the routing table, there is the fact that a path from the router to this destination address exists.
Conventionally, in a communication network which uses IP (referred to below simply as an ‘IP network’), which path is used to transmit a packet is controlled (i.e., is path-controlled) by a routing protocol. By monitoring this routing state, network operators try to become aware as quickly as possible when a failure occurs on a path in the IP network and to also ascertain when this path is restored, and to thereby achieve stable running of the IP network. Because of this, network operators may on occasion investigate the routing table of a router during an IP communication failure investigation of their own host AS.
The following two methods are known as examples of conventional routing table investigation methods. The first method is to login directly to each router within the host AS, and to give a command to read the routing table therein. The second method is to use a software tool to read the routing table in a router. More specific information can be found by referring to the Internet website “http://www.nanog.org/lookingglass.html” (this address was valid as of Jun. 6, 2007). In the method which uses software tools, an interface to the command line of the router is presented to a user. By inputting a router command on the web on which this tool is operating, the tool logs in to the router and executes the input command, and then displays the results of this action. As a result, a user is able to investigate the routing table of a router without logging in directly to the router.
However, in the above described conventional routing table investigation methods, the problems described below exist that cause a reduction in the work efficiency of the routing table investigation.
(1) Because a user logs into a router and executes a command, in some cases there is a delay in the response to the command such as when there is a heavy burden on the router or when the network traffic is heavy. In this case, there is a delay between when the network operator inputs the command and when the routing table is displayed, which leads to a deterioration in work efficiency.(2) Because each one of a plurality of routers inside the AS is logged onto individually and then executes the command individually, considerable time is needed for a network operator to refer to the routing tables of all the routers.(3) If a large number of commands are executed within a short time span, there is a possibility that an excessive load will be placed on the router.(4) Although it is possible to obtain a routing table at the time when the command is executed, it is naturally not possible to obtain past routing tables. Because of this, it is not possible to compare the current path state with past path states.